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Dec. 13, 2011 -- In some respects, the U.S. is winning the war on cancer. Recent reports show an overall decline in the number of new cancer cases and fewer cancer deaths.

But those gains aren’t being shared by everyone. A case in point: A new study shows that rates of colon and rectal cancers have climbed in younger adults over the last decade.

That’s happening even as colorectal cancer rates have dropped steadily in adults over 50, the age most people are advised to start screening for the disease.

Researchers aren’t sure what’s causing the increase in younger adults. But they hope their study will raise awareness among younger patients and their doctors, who may dismiss cancer as a cause of their symptoms.

“These young people are getting ignored. They’ve had symptoms for a year or a year and a half before they finally get diagnosed,” says researcher Y. Nancy You, MD, a surgeon at the University of Texas M.D. Anderson Cancer Center in Houston.

Tracking Trends in Colon Cancer

The study looked at nearly 600,000 colorectal cancer cases reported to a national registry between 1998 and 2007.

As expected, cancer was much more common in the older age group. About 89% of the cases were seen in adults over age 50.

But while colorectal cancer cases have dropped steadily in adults over 50, they increased by more than 2% each year in younger adults.

To compound the problem, doctors say many people may not suspect cancer when symptoms like bleeding, abdominal pain, or a change in bowel habits strike someone in their 30s or 40s.

“Most young people, when they have these types of symptoms, they are not thinking that they have cancer. Then they go to their physician and the physician isn’t thinking that they have cancer,” says Rebecca Siegel, MPH, an epidemiologist with the American Cancer Society in Atlanta.

The result is often a delay in diagnosis.

The study found that younger adults were more likely than older adults to be diagnosed with late-stage cancers, which are harder to treat.

People in their 30s were about 20% more likely than other age groups to be diagnosed when their cancers were stage III or IV, with stage IV being the most severe grade of the disease. Other factors that increased the risk for having an advanced cancer at diagnosis were being African-American or lacking health insurance.

“It’s cause for concern,” says Siegel, who was not involved in the study. “And hopefully, it will spur additional research to try to identify what’s causing this trend.”

The study is published in the Archives of Internal Medicine. It isn’t the first to spot the uptick, but it is the largest so far to note the increase.

Advice to Patients

Experts say the message to patients is clear: “Just because you’re under 50 doesn’t mean you’re not at risk,” says Anthony Starpoli, MD, a gastroenterologist at Lenox Hill Hospital in New York City.

“If you have a family history, go talk to your doctor,” Starpoli tells WebMD, especially if that relative got colon cancer before they were 50.